In order to efficiently support an area like a hot spot with high traffic in a Long Term Evolution (LTE) or LTE-advanced (LTE-A) radio communication system, a technique called a centralized radio access network (C-RAN) capable of accommodating a large number of cells while suppressing a device cost is known (see Non-Patent Documents 1 and 2).
The C-RAN includes one or more radio units (RUs) serving as a base station installed in a remote site and a digital unit (DU) serving as a base station that centrally controls the RUs. The DU has the layers 1 to 3 functions included in a base station. An Orthogonal Frequency Division Multiplexing (OFDM) signal generated by the DU is sampled and transmitted to the RU and then transmitted through a radio frequency (RF) function unit included in the RU.